Blow pin assembly

ABSTRACT

This invention relates to a blow pin assembly for use in extrusion blow molding processes to yield thermoplastic containers having a dripless pour lip. The dripless pour lip is achieved by forge forming a portion of the neck moil, which moil is characteristic of extrusion blow molding processes. The shape of the pour lip is dictated by a downwardly facing groove carried by a cutter collar which is part of the blow pin assembly. This groove coacts with a split annular anvil carried by the split blow mold to achieve the necessary forge forming of the container lip. The cutter collar also achieves removal of excess neck moil material by a cutting action achieved between the outside edge of the groove and the split annular anvil.

BACKGROUND OF THE INVENTION

This invention relates to a blow pin assembly for use in extrusion blow molding processes to yield thermoplastic containers having a dripless pour lip.

In conventional extrusion blow molding procedures, a hot extruded tube of thermoplastic material is captured between the mold halves of a split blow mold. This capture results in the lower end of the tube being pinched off and a portion of the upper end of the tube extending out of the split blow mold. This upper end of the tube is commonly referred to as a neck moil.

After the tube's capture, a blow pin assembly, which includes a blow pin tip, is lowered so that the tip enters into the tube to forge form the neck finish of the soon to be blown container. Also, neck moil removal procedures are contemporaneously initiated when the tip enters the tube. The neck moil removal is accomplished by providing, as part of the blow pin assembly, a cutter collar designed for making shearing contact with an anvil carried by the split blow mold. Since the neck moil is caught between the cutter collar and the anvil, its separation from the container neck finish is effected. Exemplary of such a blow pin assembly is the one described in U.S. Pat. No. 4,173,447.

Besides removal of the neck moil, the cutter collar and anvil also accomplish another function in that they also form the top and outside edge surfaces of the container lip. Conventionally, the top surface is formed in a plane and the outside edge surface is formed as a sharp corner. While such a lip configuration is widely used, it has a tendency to allow dripping when the liquid contents of the container are poured therefrom.

It has been found that this undesirable dripping can be mitigated by providing a lip which has a rounded top surface. Production of such a lip, however, will require a different apparatus than hereinabove described.

Therefore, it is an object of this invention to provide, for use in the extrusion blow molding of thermoplastic containers, a blow pin assembly which provides a rounded container lip and which effects neck moil removal.

THE INVENTION

This invention relates to an apparatus for providing a rounded, dripless pour lip on an extrusion-blow molded thermoplastic container. The apparatus features a split annular anvil which is mounted to a split blow mold. The split blow mold defines a hollow mold space and is designed for use in the extrusion-blow mold process. Coacting with the split annular anvil there is also provided a blow pin assembly which is reciprocally movable along the vertical axis of the hollow mold space. The blow pin assembly has a blow pin stem having a bore therethrough for the passage of blow air. Mounted to the blow pin stem are a hollow blow pin tip and a cutter. The blow pin tip is mounted to the distal end of the blow pin stem while the cutter is mounted at a position above the blow pin tip. The diameter of the blow pin tip is less than the inside diameter of the split annular anvil. A feature of the cutter is its annular downwardly facing groove. This groove is utilized in forming the rounded, dripless pour lip and in removing the neck moil formed by the extrusion-blow mold process. Configurationwise, the annular groove has an inside diameter less than and an outside diameter greater than the inside diameter of the split annular anvil. The groove, at its outermost extent, is dimensioned to make neck moil cutting contact with the split annular anvil when the blow pin assembly is lowered to place the blow pin tip within the neck finish defining portion of the hollow mold space. To provide the rounded configuration for the dripless, pour lip the groove also features a concave surface which will forge form the rounded part of the pour lip when the blow pin assembly is lowered to the just described position.

In a preferred form the split annular anvil of this invention has an annular vertical wall defining its inside diameter and an annular top wall which slopes downwardly and outwardly from the upper extent of the annular vertical wall. In this preferred embodiment, the groove, at its outside diameter, will achieve its neck moil cut by making contact with the annular top wall of the split annular anvil.

These and other features of this invention contributing to satisfaction in use and economy of manufacture will be more fully understood from the following description and accompanying drawings in which identical numerals refer to identical parts and in which:

FIG. 1 is a sectional view showing the apparatus of this

invention in association with a split blow mold;

FIG. 2 is a top plan view of the anvil shown in FIG. 1;

FIG. 3 is a sectional view taken through sectional lines 3--3 in FIG. 2; and

FIG. 4 is a bottom plan view of the cutter shown in FIG. 1.

Referring now to FIGS. 1-4 there can be seen an apparatus of this invention, generally designated by the numeral 10, in association with a split blow mold, generally designated by the numeral 12. Split blow mold 12 comprises two mold halves 42 and 44. As is conventional in the art mold halves 42 and 44 are powered for reciprocal movement towards and away from the center axis defined by the mold cavity which is formed when mold halves 42 and 44 are brought together.

Apparatus 10 comprises a blow pin assembly, generally designated by the numeral 16, and a split annular anvil, generally designed by the numeral 14. Split annular anvil 14 is comprised of two anvil halves 34 and 36, as can be seen in FIGS. 2 and 3. Anvil halves 34 and 36 are mounted to mold halves 42 and 44 respectively by bolting. Facilitating this bolting attachment there is provided bolt bores 48, 48a, 48b, and 48c. Other conventional modes of mounting can also be used. When the split anvil halves are brought together by the closing of mold halves 42 and 44, as shown in FIG. 1, they form together split annular anvil 14 which has a vertical annular inside wall 38. Furthermore, split annular anvil 14 additionally has annular top wall 40 which slopes outwardly and downwardly from the uppermost extent of vertical annular inside wall 38. Note that the inside diameter of split annular anvil 14, as defined by vertical annular inside wall 38, is greater than the diameter of blow pin 24, hereinafter described, but less than the diameter of neck finish 45.

Partially positioned within neck finish 45 is blow pin assembly 16. Blow pin assembly 16 features a blow pin stem 18 which has an upper portion 20 and a lower portion 22. Upper portion 20 has a rectangular cross-section while lower portion 22 is circular in cross section. Lower portion 22 also has, at its distal end, threads 23. Blow pin stem 18, for the embodiment shown in the drawings, has a concentric bore therethrough for the passage of blow air.

Slidably mounted onto upper portion 20 of blow pin stem 18 is cutter collar 15. As can be seen in FIG. 4, cutter collar 15 has a rectangular bore 46 therethrough. Rectangular bore 46 is dimensioned to effect slidable mounting of cutter collar 15 to upper portion 20 of blow pin stem 18. By utilizing the rectangular bore and rectangular upper portion 20, it is possible to fixedly mount cutter collar 15 to blow pin stem 18 whereby rotation of blow pin stem 18 effects rotation of cutter collar 15.

Cutter collar 15 has an annular, downwardly facing groove 26 as shown in FIGS. 1 and 4. Annular groove 26 has an inside edge 28 and an outside edge 32. Also defining groove 26 is concave surface 30. As can be seen in FIG. 1, for the embodiment shown, groove 26 has an inverted "U" shape when viewed in axial cross section. Inside edge 28 of groove 30 has a diameter less than the diameter of vertical annular inside wall 38. On the other hand, outside edge 32 has a diameter greater than the diameter of vertical annular inside wall 38.

Threadedly attached to blow pin stem 18 at its lower portion 22 is blow pin tip 24. Blow pin tip 24 has a partially threaded bore for cooperation with thread 23 at the distal end of lower portion 22.

In operation, a hot thermoplastic extruded tube is captured between split blow mold 12 by the closing of mold halves 42 and 44 on the tube. The lower end of the tube is pinched off while the upper end of the tube extends outward of split blow mold 12 to yield a neck moil, labelled by the letter "A" in FIG. 1. Subsequent to the capture of the tube, blow pin assembly 16 is lowered so that blow pin tip 24 forges the hot tube to conform to the shape defined by neck finish 45. As can be seen in FIG. 1, for the embodiment shown, a helical thread is formed on the neck finish. Also, by the lowering of blow pin 24 cutter collar 15 is also lowered thereby bringing groove 26 into contact with neck moil "A". Some of the neck moil will be captured within the cavity defined by groove 26 so that it is forge formed into the shape dictated by the groove. Since groove 26 has concave surface 30, the lip of the container will take on a rounded shape. Contemporaneous with the forge forming of the container lip there is also accomplished removal of neck moil "A" by the cutting action realized when outside edge 32 strikes top wall 40 of split annular anvil 14. To insure high fidelity separation of neck moil "A" from container "B", blow pin stem 18 can be rotated back and forth thereby causing a rotative cutting action between outside edge 32 and top wall 40. Subsequent to or contemporaneously with the above described lip formation and moil removal, blow air can be introduced into the extruded tube via the concentric bore of blow pin stem 18 to blow form bottle "B".

It has been found advantageous to have annular vertical wall 38 with a diameter smaller than the outside diameter of neck finish 45 for the reason that the split annular anvil will project to some extent under the rounded lip being formed so that structural support is provided for the forge forming of the lip. Also note that outside edge 32 is, for the embodiment shown, in a plane with inside edge 28. It is to be understood, however, that this coplanar relationship is not necessary, it being contemplated that outside edge 32 can be above or below inside edge 28. 

I claim:
 1. An apparatus for providing a rounded, dripless pour lip on a thermoplastic container blow molded from an extruded tube, said apparatus comprising:A. a split annular anvil,i. having a single annular vertical wall defining its inside diameter, ii. having an annular top wall which slopes downwardly and outwardly from the upper extent of said annular vertical wall, iii. being mounted to a split blow mold, said split blow mold defining a hollow mold space including a neck finish defining portion and being adapted for the capture of and the blow molding of said extruded tube, iv. said inside diameter of said annular anvil being smaller than the inside diameter of said neck finish defining portion of said split blow mold to thereby provide a neck finish on said blow molded container having a vertical wall annular recess in the outer wall of said neck finish at the uppermost end thereof; B. a blow pin assembly reciprocally movable along the vertical axis of said hollow mold space, said blow pin assembly comprising,i. a blow pin stem having a bore for the passage of blow air therethrough, ii. a hollow blow pin tip mountable to the distal end of said blow pin stem and having an outside diameter less than said inside diameter of said split annular anvil, and iii. a cutter mounted to said blow pin stem at a position above said blow pin tip, said cutter having an annular downwardly facing groove which has the shape of an inverted "U" when said groove is viewed in axial section and having,a. an inside diameter less than and an outside diameter greater than said inside diameter of said split annular anvil but less than the diameter of said neck finish defining portion of said split blow mold, wherein said groove at its outside diameter makes neck moil cutting contact with said annular top wall of said split annular anvil when said blow pin assembly is lowered to position said blow pin tip within the neck finish defining portion of hollow mold space, and b. a concave surface for forge forming the rounded part of said dripless pour lip on the upper portion of said captured extruded tube, said concave surface being located between said inside diameter and said outside diameter of said groove.
 2. The apparatus of claim 1 wherein said inside diameter of said groove is substantially equal to said outside diameter of said blow pin tip.
 3. The apparatus of claim 2 wherein said blow pin tip and said cutter are in abutment one with the other.
 4. The apparatus of claim 1 wherein said cutter is fixedly mounted to said blow pin stem whereby rotation of said blow pin stem imparts like rotative motion to said cutter. 